Many theories have been proposed to understand the etiology and progression of myofascial pain dysfunction (MPD) and temporomandibular joint internal derangments (TMJ ID), but more research is required to support or refute them. The aims of this study are to: 1) Determine the prevalence and natural stages of progression of MPD and TMJ ID and 2) Determine the association that the following proposed etiologic factors, oral parafunctional habits, occlusal disharmony, stressful life events and the combination of these factors have on this prevalence and progression. A longitudinal epiedemiological study of these factors in 260 female nursing students will be used to accomplish this study's aims. The initial cross sectional study of these subjects was accomplished in the Fall of 1984, with followup evaluations scheduled after 18 and 36 months using an identical protocol. The Craniomandibular Index (CMI) and the Symptom Severity Index (SSI) are measures used to assess objective and subjective severity of pain and dysfunction. The Oral Habit Index, and the Occlusal Disharmony Index, and the Social Readjustment Rating Scale are measures used to assess subjective and objective indicators of oral parafunctional habits, occlusal stability and function, and the number and severity of stressful life events. In addition to measuring severity of pain and dysfunction with the CMI and SSI, subjects will be classified using specific criteria into one of nine progressively more severe diagnostic classifications that include: three MPD classifications, five TMJ ID classifications, or non-illness control. The progression or regression of MPD and TMJ ID will be determined by the change in CMI, SSI, and the change from one diagnostic classification to another. The relationship that oral parafunctional habits, occlusal disharmony, and stressful life events, or a combination of these factors have with this progression or regression will be determined in two ways. First, the association between individual and combinations of these factors and the change in pain and dysfunction will be determined. Second, scores of each factor for those subjects whose pain and dysfunction were worse versus those who were the same or better will be compared. The results will be used to help predict the consequences of non-treatment and determining additional factors that need to be addressed as treatment proceeds.